Technical Abstract: In agricultural, rangeland, and forest system revegetation projects, cover crops are used for competitive exclusion of weeds and to stabilize soil. Within revegetation projects, annual or short-lived perennial grasses are often sown at the same time as the perennial grasses that are the desired species for long-term landscape rehabilitation. When cover crops are utilized to control weeds, the same principle of competitive exclusion may apply to sown perennial grasses. In this project, we tested if the presence of an annual grass cover crop reduces the early stage performance of sown perennial grasses. We conducted four experiments to evaluate the affects of annual cover crops on perennial grasses. The experiments included ex situ growth chamber experiments in two soil types: an agronomic soil and soil collected from a revegetation project in a trenched water pipeline in western North Dakota. We also performed two in situ experiments where the presence of annuals was manipulated. Annual cover crops only reduced perennial grass biomass ex situ in the agronomic soil. The disturbed pipeline soil was high in sulfur and sodium. Even when this soil was fertilized, annual cover crops did not reduce sown perennial performance. In stressful environments, or when there is natural microenvironmental variability, annual cover crops do not appear to be costly for the early-stage establishment of more long-term, desirable species.